Jing Ouyang

Palladium nanoparticles deposited on silanized halloysite nanotubes: synthesis, characterization and enhanced catalytic property

Palladium (Pd) nanoparticles were deposited on the surface of halloysite nanotubes (HNTs) modified with γ-aminopropyltriethoxysilane (APTES) to produce Pd/NH2-HNTs nanocomposites. The results indicated that Pd nanoparticles were densely immobilized onto NH2-HNTs with an average diameter of ~ 3 nm. The Pd distribution on the surface of silanized HNTs showed much more uniform, and the Pd nanoparticle size became smaller compared with those directly deposited onto HNTs without silanization. Systematic characterization demonstrated that APTES were chemically bonded onto HNTs, and further confirmed the bond formation between Pd and -NH2 groups, which could ensure the firm deposit of Pd nanoparticles on the surface of silanized HNTs. The as-synthesized Pd/NH2-HNTs exhibited an excellent catalytic activity in the liquid-phase hydrogenation of styrene to ethylbenzene with full conversion within 30 min. The mechanism of the deposit of Pd nanoparticles on silanized HNTs was also investigated.

From Natural Attapulgite to Mesoporous Materials: Methodology, Characterization and Structural Evolution

In this paper, we report the synthesis of hexagonally ordered aluminum-containing mesoporous silica, Al-MCM-41, from natural attapulgite (Al-substituted Si(8)O(20)Mg(5)(OH)(2)(H(2)O)(4) x 4 H(2)O) without addition of silica or aluminum reagents. A pretreatment process involving sequential mechanical grinding and acid leaching is critical to the successful use of attapulgite as a source of both Si and Al in the surfactant-templated hydrothermal synthesis of Al-MCM-41. The resulting mesophase had a surface area of 1030 m(2)/g and an average pore diameter of 3.7 nm with narrow pore size distribution. The influence of changes in processing parameters, such as grinding time, hydrothermal conditions, and calcination temperature, on the textural characteristics of the Al-MCM-41 products is studied. Investigations of the mechanism of structural evolution indicate that grinding of attapulgite results in amorphization and partial structural breakdown, transformation of the fibrous mineral bundles into rod-shaped particles, and partial displacement of octahedrally coordinated Al(3+) ions into the Si-O tetrahedral framework. Subsequent acid etching dissolves the Mg-rich octahedral sheets to produce samples with variable texture due to modifications in the residual aluminum-containing silicate sheets and associated silica fragments. Solid-state magic-angle spinining NMR spectroscopy indicates that Al(3+) ions are located in both octahedral and tetrahedral sites in the as-synthesized Al-MCM-41 samples, but that the calcined products consist primarily of Al(3+) ions substituted in the tetrahedrally coordinated silica matrix of the ordered channel wall structure.

CuO nanoparticles encapsulated inside Al-MCM-41 mesoporous materials via direct synthetic route

Highly ordered aluminum-containing mesoporous silica (Al-MCM-41) was prepared using attapulgite clay mineral as a Si and Al source. Mesoporous complexes embedded with CuO nanoparticles were subsequently prepared using various copper sources and different copper loadings in a direct synthetic route. The resulting CuO/Al-MCM-41 composite possessed p6mm hexagonally symmetry, well-developed mesoporosity, and relatively high BET surface area. In comparison to pure silica, these mesoporous materials embedded with CuO nanoparticles exhibited smaller pore diameter, thicker pore wall, and enhanced thermal stability. Long-range order in the aforementioned samples was observed for copper weight percentages as high as 30%. Furthermore, a significant blue shift of the absorption edge for the samples was observed when compared with that of bulk CuO. H2-TPR measurements showed that the direct-synthesized CuO/Al-MCM-41 exhibited remarkable redox properties compared to the post-synthesized samples, and most of the CuO nanoparticles were encapsulated within the mesoporous structures. The possible interaction between CuO and Al-MCM-41 was also investigated.

Perovskite LaFeO3/montmorillonite nanocomposites: synthesis, interface characteristics and enhanced photocatalytic activity.

Perovskite LaFeO3/montmorillonite nanocomposites (LaFeO3/MMT) have been successfully prepared via assembling LaFeO3 nanoparticles on the surface of montmorillonite with citric acid assisted sol-gel method. The results indicated that the uniform LaFeO3 nanoparticles were densely deposited onto the surface of montmorillonite, mainly ranging in diameter from 10 nm to 15 nm. The photocatalytic activity of LaFeO3/MMT was evaluated by the degradation of Rhodamine B (RhB) under visible light irradiation, indicating that LaFeO3/MMT exhibited remarkable adsorption efficiency and excellent photocatalytic activity with the overall removal rate of RhB up to 99.34% after visible light irradiation lasting for 90 min. The interface characteristic and possible degradation mechanism were explored. The interface characterization of LaFeO3/MMT suggested that LaFeO3 nanoparticles could be immobilized on the surface of montmorillonite with the Si-O-Fe bonds. The abundant hydroxyl groups of montmorillonite, semiconductor photocatalysis of LaFeO3 and Fenton-like reaction could enhance the photocatalytic degradation through a synergistic effect. Therefore, the LaFeO3/MMT is a very promising photocatalyst in future industrial application to treat effectively wastewater of dyes.

Enhanced performance and interfacial investigation of mineral-based composite phase change materials for thermal energy storage

A novel mineral-based composite phase change materials (PCMs) was prepared via vacuum impregnation method assisted with microwave-acid treatment of the graphite (G) and bentonite (B) mixture. Graphite and microwave-acid treated bentonite mixture (GBm) had more loading capacity and higher crystallinity of stearic acid (SA) in the SA/GBm composite. The SA/GBm composite showed an enhanced thermal storage capacity, latent heats for melting and freezing (84.64 and 84.14 J/g) was higher than those of SA/B sample (48.43 and 47.13 J/g, respectively). Addition of graphite was beneficial to the enhancement in thermal conductivity of the SA/GBm composite, which could reach 0.77 W/m K, 31% higher than SA/B and 196% than pure SA. Furthermore, atomic-level interfaces between SA and support surfaces were depicted, and the mechanism of enhanced thermal storage properties was in detail investigated.

Carbon hybridized halloysite nanotubes for high-performance hydrogen storage capacities

Hybrid nanotubes of carbon and halloysite nanotubes (HNTs) with different carbon:HNTs ratio were hydrothermally synthesized from natural halloysite and sucrose. The samples display uniformly cylindrical hollow tubular structure with different morphologies. These hybrid nanotubes were concluded to be promising medium for physisorption-based hydrogen storage. The hydrogen adsorption capacity of pristine HNTs was 0.35% at 2.65 MPa and 298 K, while that of carbon coated HNTs with the pre-set carbon:HNTs ratio of 3:1 (3C-HNTs) was 0.48% under the same condition. This carbon coated method could offer a new pattern for increasing the hydrogen adsorption capacity. It was also possible to enhance the hydrogen adsorption capacity through the spillover mechanism by incorporating palladium (Pd) in the samples of HNTs (Pd-HNTs) and 3C-HNTs (Pd-3C-HNTs and 3C-Pd-HNTs are the samples with different location of Pd nanoparticles). The hydrogen adsorption capacity of the Pd-HNTs was 0.50% at 2.65 MPa and 298 K, while those of Pd-3C-HNTs and 3C-Pd-HNTs were 0.58% and 0.63%, respectively. In particular, for this spillover mechanism of Pd-carbon-HNTs ternary system, the bidirectional transmission of atomic and molecular hydrogen (3C-Pd-HNTs) was concluded to be more effective than the unidirectional transmission (Pd-3C-HNTs) in this work for the first time.

Natural halloysite nanotubes modified as an aspirin carrier

Natural halloysite nanotubes (HNTs) modified with 3-aminopropyltriethoxysilane were used as an aspirin carrier. The structure, drug loading and release profiles of samples were characterized by X-ray diffraction (XRD), thermogravimetry-differential scanning calorimetry (TG-DSC), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and UV-spectrophotometry. The Higuchi model Q = kt0.5 was employed to analyze the dissolution data in detail. The results indicated that the modification of HNTs could improve the amount of aspirin from 3.84 to 11.98 wt%. The physical state of aspirin was nanocrystalline and amorphous affected by the confined space of HNTs, which significantly enhanced the dissolution rate created by a burst release within the first hour. The linearity of the Higuchi equation indicated that the aspirin release mechanism for modified HNTs was fitted to Ficks diffusion and the dissolution rate was slower than that of natural HNTs. The as-synthesized N-HNTs could have interesting potential application in drug carrier systems.

Assembling strategy to synthesize palladium modified kaolin nanocomposites with different morphologies.

Nanocomposites of aluminosilicate minerals, kaolins (kaolinite and halloysite) with natural different morphologies assembling with palladium (Pd) nanoparticles have been successfully synthesized through strong electrostatic adsorption and chemical bonding after surface modification with 3-aminopropyl triethoxysilane (APTES). Meanwhile, the influence of different morphologies supports on catalytic hydrogenation properties was explored. The surface concentration of amino groups on the kaolins was related to the morphology and surface nature. Electronmicroscopy revealed that the monodisperse Pd nanoparticles were uniformly deposited onto the surface of kaolins, ranging in diameter from 0.5 nm to 5.5 nm. The functional groups could not only improve the dispersion of kaolins with different morphologies in solution, but also enhance the interaction between Pd precursors and kaolins, thus preventing small Pd nanoparticles from agglomerating and leading to high activity for the catalytic hydrogenation of styrene. Pd-FK@APTES was more active compared to other samples. Selecting the kaolin morphology with a different surface nature allows the selective surface modification of a larger fraction of the reactive facets on which the active sites can be enriched and tuned. This desirable surface coordination of catalytically active atoms could substantially improve catalytic activity.

Hierarchical MoS2 intercalated clay hybrid nanosheets with enhanced catalytic activity

Emerging hierarchical MoS2/pillared-montmorillonite (MoS2/PMMT) hybrid nanosheets were successfully prepared through facile in-situ hydrothermal synthesis of MoS2 within the interlayer of cetyltrimethylammonium bromide PMMT, and their catalytic performance was evaluated by the reduction reaction of 4-nitrophenol (4-NP) using NaBH4 as a reductant. Microstructure and morphology characterization indicated that MoS2/PMMT exhibited hybrid-stacked layered structures with an interlayer spacing of 1.29 nm, and the MoS2 nanosheets were intercalated within the montmorillonite (MMT) layers, with most of the edges exposed to the outside. The catalytic activity and stability of MoS2/PMMT were both enhanced by the MMT. With the MoS2/PMMT as the catalyst, the apparent reaction rate constant of the 4-NP reduction was 0.723 min−1 and was maintained at ~0.679 min−1 after five reaction cycles. The structural evolution of MoS2/PMMT and the possible catalysis mechanism for the reduction reaction of 4-NP were investigated. The as-prepared MoS2/PMMT hybrid nanosheets are promising candidates for catalytic application in the water-treatment and biomedical fields. The strategy developed in this study can provide insights for designing hybrid nanosheets with diverse heterogeneous two-dimensional (2D) nanomaterials.

Acid-hybridized expanded perlite as a composite phase-change material in wallboards

Form-stable composite phase change materials (PCMs) for use in wallboards were prepared by absorbing stearic acid (SA) and lauric acid (LA) eutectic mixtures into the pores of expanded perlite (EP) via vacuum impregnation. The microstructure, thermal properties and the thermal reliability of the composite PCMs were characterized by thermogravimetric and differential scanning calorimetry, X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. The results indicate that the maximum SA–LA absorption of the EP was as high as 65 wt% without any melted SA–LA leakage. The latent heat of the composite PCMs was 119.0 J g−1 at its melting temperature of 31.69 °C and 117.4 J g−1 at its freezing temperature of 30.01 °C. A thermal cycling test showed that the composite PCMs have excellent structural stability and thermal reliability after 100 melt–freeze cycles. A gypsum-based building wallboard containing 6 wt% SA–LA/EP had a low density (0.924 g cm−3), high mechanical strength (2.19 MPa), and remarkable heating preservation performance. These properties indicate that the composite PCMs that we used for wallboards can be considered an efficient heating preservation material for practical applications in building energy conservation.